Method and arrangement for identifying optical aberrations

Abstract

It is provided a method for identifying optical aberrations. The method comprising the steps of providing at least one first optical beam and a second optical beam; creating a combined beam by at least partially superimposing the first and the second optical beam; focusing the combined beam into or through a medium and detecting radiation excited in the medium by the combined beam due to nonlinear optical effects; detecting the radiation excited in the medium by the combined beam for each one of the phase positions, the spatial positions and/or the time positions of the first beam; and identifying aberrations using signals generated by a detection device for the plurality of the phase positions, the spatial positions and/or the time positions of the first beam relative to the second beam upon the detection of the radiation excited in the medium.

The invention claimed is: 
     
       1. A method for identifying optical aberrations, comprising the steps of:
 a) providing at least one first optical beam and a second optical beam, wherein the intensity of one of the optical beams is higher than the intensity of the other optical beam; 
 b) creating a combined beam by at least partially superimposing the first and the second optical beam; 
 c) focusing the combined beam into or through a medium and detecting radiation excited in the medium by the combined beam due to nonlinear optical effects; wherein 
 d) the first beam is shifted in phase relative to the second beam to a plurality of phase positions, the first beam is spatially displaced relative to the second beam to a plurality of spatial positions and/or the first beam is temporally shifted relative to the second beam to a plurality of time positions; 
 e) detecting the radiation excited in the medium by the combined beam for each one of the phase positions, the spatial positions and/or the time positions of the first beam, wherein the radiation is detected by means of a detection device; and 
 f) identifying aberrations, using a processor, the aberrations being identified using signals generated by the detection device for the plurality of the phase positions, the spatial positions and/or the time positions of the first beam relative to the second beam upon the detection of the radiation excited in the medium. 
 
     
     
       2. The method as claimed in  claim 1 , wherein the aberrations are identified using at least first signals generated by the detection device upon detecting radiation for a first phase position, a first spatial and/or a first time position of the first beam and using second signals generated by the detection device upon detecting radiation for a second phase position, a second spatial and/or a second time position of the first beam. 
     
     
       3. The method as claimed in  claim 1 , wherein identifying aberrations according to step f) comprises determining a point spread function. 
     
     
       4. The method as claimed in  claim 1 , wherein at least a first and second measurement of the radiation excited in the medium is carried for each one of the spatial positions of the first beam, wherein the relative phase between the first and the second beam is altered between the first and the second measurement. 
     
     
       5. The method as claimed in  claim 1 , wherein the identified aberrations are used for correcting the wavefront of the first and/or second optical beam in order to obtain a corrected first and/or second beam. 
     
     
       6. The method as claimed in  5 , wherein the corrected first and/or second beam is used as a measurement beam for investigating the medium. 
     
     
       7. The method as claimed in  claim 1 , wherein identifying aberrations according to step f) comprises determining an estimate of the aberrations on the basis of the signals of the detection device; correcting the first beam by correcting the wavefront of the first beam using the estimate; and repeating steps d) to f) using the corrected first beam in order to get an improved estimate of the aberrations. 
     
     
       8. The method as claimed in  claim 1 , wherein multiple second beams are provided for generating the combined beam. 
     
     
       9. The method as claimed in  claim 1 , wherein the intensity of one of the optical beams is at least three times, at least five times or at least ten times the intensity of the other optical beam. 
     
     
       10. The method as claimed in  claim 1 , wherein the first optical beam is a scanning beam and the second optical beam is stationary. 
     
     
       11. The method as claimed in  claim 1 , wherein the first and the second optical beam are pulsed beams. 
     
     
       12. An arrangement for identifying optical aberrations comprising:
 a beam generating device for generating at least one first optical beam and a second optical beam in such a way that the intensity of one of the optical beams is higher than the intensity of the other optical beam; 
 a superimposing arrangement for at least partially superimposing the first and the second optical beam to form a combined beam; 
 a focusing device for focusing the combined beam into or through a medium and a detecting device for detecting radiation excited in the medium by the combined beam due to nonlinear optical effects; 
 a scanning device for phase shifting the first beam relative to the second beam to a plurality of phase positions, for spatially displacing the first beam relative to the second beam to a plurality of spatial positions and/or for temporally shifting the first beam relative to the second beam to a plurality of time positions, wherein the detecting device is configured in such a way that the radiation excited in the medium by the combined beam is detected for each one of the phase positions, the spatial positions and/or the time positions of the first beam; and 
 an evaluation device comprising a processor configured for identifying aberrations using signals generated by the detecting device for the plurality of the phase positions, the spatial positions and/or the time positions of the first beam relative to the second beam upon detection of the radiation excited in the medium. 
 
     
     
       13. The arrangement as claimed in  claim 12 , wherein the beam generating device comprises a light source for generating an optical beam and a beam splitter for splitting the optical beam into the first and the second optical beam. 
     
     
       14. The arrangement as claimed in  claim 12 , further comprising a wavefront shaping device configured for shaping the wavefront of the first and/or second optical beam and/or a temporal profile shaping device for shaping the temporal profile of the first and/or second optical beam using the aberrations identified by the evaluation device. 
     
     
       15. The arrangement as claimed in  claim 12 , further comprising a device for varying the optical path of the second optical beam. 
     
     
       16. An optical system comprising the arrangement as claimed in  claim 12 .